The present invention relates to a optical recording medium, an optical recording method, an optical reproducing method, an optical recording device, an optical reproducing device, and an optical recording/reproducing device.
As a conventional optical recording medium, for example, a CD (Compact Disk) used for, e.g., an audio system, a game program, or the like, or a so-called ROM (Read Only Memory) type disk which is used in only reproduction in an optical disk such as a DVD (Digital Versatile Disk) for a video system or the like is known.
Information recording in such an optical recording medium is performed such that a recording portion, e.g., an uneven pits, a wobbling groove, or the like in which information is recorded as a change in physical shape in one of a direction of thickness or a direction of track width is formed, and an Al reflective film is coated to be able to read the information of the recording portion with a high optical S/N.
In the optical recording medium having the recording portion which is subjected to the change in physical shape, for example, the recording portion is formed synchronously with molding of a plastic substrate by, e.g., injection molding, or the recording portion is formed by a 2P method (Photopolymerization method) on, e.g., a plastic substrate. For this reason, the optical recording medium can be advantageously manufactured at low cost in mass production.
Therefore, it is a problem that copying of the optical recording medium of this type is performed without using a proper route, i.e., copying is performed without permission of a copyright holder. Since reading for the optical recording medium is performed without contact, a deterioration in characteristic rarely occurs even through the optical recording medium is repeatedly used. Therefore, the sale is performed without using a proper route such that a used optical recording medium is sold as a new optical recording medium. Similarly, the sale is performed without permission of a copyright holder, disadvantageously.
The optical recording medium of this type is desired such that the additional recording of a cipher, a mark, or the like serving as a means for judging whether the optical recording medium is obtained through a proper route on a maker side can be performed.
For example, in a game, it is desired by users that an optical recording medium has such a function that an end point of the game can be recognized when the game is temporarily ended. It is desired that simple recording such as recording of personal information of a user can be performed on a user side.
In addition, it is desired by makers and users that an optical recording disk has a function of correcting some data stored in the disk after the disk is manufactured or a function of partially adding new data. For example, in a satellite navigation system, when the additional functions are added, a simple change of a map and additional information are transmitted from a maker or are inputted by a user herself/himself as data, so that the change and the information can be recorded on a disk by the user.
A conventional recording medium in which conventional optical recording can be performed, e.g., a CD-R in which additional recording can be performed only once is manufactured such that a coloring material is coated on a plastic substrate having a guide groove by a spin coat method, and Au is sputtered on the plastic substrate.
A programmable photomagnetic recording medium is manufactured such that a transparent dielectric film, a vertical magnetized film consisting of TbFeCo serving as a recording material, a transparent dielectric film, and an Al reflective film are sequentially sputtered.
A rewritable phase change recording medium is formed by using a phase change material such as GeSbTe serving as a recording material in the configuration of the rewritable optical recording medium.
However, all the recording media described above are expensive. In the rewritable optical recording medium, the number of steps in manufacturing the rewritable optical recording medium is large because a large number of films must be formed as described above. When an additional recording layer is formed by using each of these materials as a recording material, the rewritable optical recording medium is more expensive than the ROM type optical recording medium such as a CD described above.
It is an object of the present invention to provide an optical recording medium, an optical recording method, an optical reproducing method, an optical recording device, an optical reproducing device, and an optical reproducing device which can be inexpensively manufactured by a configuration and a manufacturing method corresponding to a ROM type configuration described above and which make it possible to perform additional description of the cipher, the mark, and the like described above.
An optical recording medium having an information layer with a reflective film on which an information recording portion is formed by physical change of shape at least in one direction of depth and track width, wherein said reflective film having such an a structure that additional recording can be performed by thermal recording, and that the reflectance of said reflective film changes in the range of 0.5% less than (|R0xe2x88x92R1|/R0)xc3x97100% less than 17%, where R0 is reflectance of non-recording state and R1 is reflectance of recording state for reproducing beam.
The optical recording medium of claim 1, characterized in that if the additional recording region of said reflective film is at least partially overlapped with said information recording portion formed by physical change of shape, the reflectance of said reflective film changes in the range of 0.5% less than (|R0xe2x88x92R1|/R0)xc3x97100% less than 10%.
According to a method of optical recording of the present invention, the thermal recording for additional recording is performed on optical recording medium of the present invention as described above by irradiation of laser light which is modulated by additional recording information signal, to change or to increase or decrease the reflectance of reflective film due to the change of quality of the reflective film, e.g. the movement of atoms, the change of crystal structure or the like.
According to a method of optical reproducing of the present invention, on the optical recording medium of the present invention as described above on which additional recording has been performed by changing of the reflectance of reflective film, laser beam is irradiated to reproduce the additional recording by the micro change of return light due to the change of reflectance.
Further, an optical recording apparatus of the present invention has optical recording means for performing additional recording on the additional recording region of the reflective film of the optical recording medium of the present invention as described above. The optical recording means has laser irradiation means for irradiating laser beam which is modulated in response to the additional recording information on the optical recording medium and the additional recording can be performed by thermal recording which is due to the change of reflectance through the change of quality of the reflective film by irradiation of laser beam.
Furthermore, an optical reproducing apparatus is applied to reproduce additional recording which has been recorded by the change of reflectance on the reflective film of the optical recording medium of the present invention as described above, and the optical reproducing apparatus has optical reproducing means which has means for irradiating reproducing beam on the optical recording medium and detection means for detecting the return beam from the reflective film, the micro changes in the detection output of the detection means being reproducing signal of additional recording.
An optical recording reproducing apparatus of the present invention has the optical recording means of the optical recording apparatus and the optical reproducing means of the optical reproducing apparatus described above.
As described above, an optical recording medium of the present invention has an information recording portion on which physical change of shape, for example uneven pits, wobbling grooves or the like for maintaining information. It is possible to form additional recording region on optical recording medium on which reflective film has been mounted, only by selecting the property of the reflective film without increasing the number of film. Therefore, it can be manufactured at low cost and in mass production similar to the conventional CD-ROM or DVD-ROM without the number of production processes.
The additional recording method and reproducing method to the optical recording medium according to the present invention can be performed in a simple way and therefore the optical recording apparatus, optical reproducing apparatus and optical recording reproducing apparatus are composed as a simple structure.
According to the present invention, the additional recording is performed under the condition 0.5% less than (|R0xe2x88x92R1|/R0)xc3x97100% less than 17%,xe2x80x94where R0 is reflectance of reproducing beam in respect to the non-recording state, and R1 is reflectance of recording state. In case that the additional recording region is overlapped by the aforementioned information recording portion, 0.5% less than (|R0xe2x88x92R1|/R0)xc3x97100% less than 10%. The recording is performed with such a small change of reflectance, the reproducing output can be smaller than the output of reproducing information, for example, data information from the essential recording portion. Accordingly, as can be seen from the description hereinafter, the reproduction or reading of the additional recording information can be performed without disturbing the reproduction of information, for example, date information from the essential recording portion.
The additional recording can be performed by a small range of change in reflectance and therefore S/N is small on the reproduction of the additional recording. However, since the additional recording is used for cipher, mark or the like, it is required that the output is enough to read the recording and high S/N ratio is not required.
As described above, according to the present invention, in case that the additional recording region is not formed in the information recording region of the reflective film, (|R0xe2x88x92R1|/R0)xc3x97100% is equal to or less than 17%. The reason of such condition is the following. If the reflectance is varied due to recording, focusing and tracking servo should follow stably to the change of reflectance. Generally, a stable servo can be achieved as much as the change of reflectance is small in additional recording.
For example, in case of ROM disk such as DVD, the reflectance is set to 60%-85%. If the disk has a reflectance in this range, a stable servo can be achieved without adding a high servo circuit. By selecting the mean value of 60%-85%, or 72.5% as the circuit constant of the servo circuit, the maximum variation of the reflectance, if it exits, is (72.5xe2x88x9260)/72.5xc3x97100=17%. Therefore, a simple circuit can achieve servo. If simple recording is performed partially in the additional recording, 17% of the reflectance of the same level is desirable.